Team-BHP > Buckle Up > 4x4 & Off-Roading > 4x4 Technical


View Poll Results: Poll canceled.
option 1 0 0%
option 2 0 0%
Multiple Choice Poll. Voters: 14. You may not vote on this poll

Reply
 
Thread Tools Search this Thread
Old 16th November 2018, 17:04   #271
BHPian
 
Join Date: Apr 2016
Location: Delhi NCR
Posts: 65
Thanked: 118 Times
Default Re: Torque generation and distribution

Dear Experts,

I had posted the following query on the thread "Ford Endeavour: Official Review".
"How much peak Torque does the 3.2 Endeavour produce in 4x4 Low mode?"
After an explanation by a fellow BHpian who stated that the Torque figure does not change and remains the same in all gears though available at a lower range of RPM, I did some more research which threw up the concept of Torque Multiplication in 4x4 Low Range and I wrote a more detailed post as under:
"Ok, let me first state the reason why I had asked this question in the first place. While test-driving the Pajero Sport manual some months back, the sales person had told me that the Pajero Sport in 4x4 LLC mode would be producing more than 900 NM of torque, which should be able to cross any hurdle / very difficult hurdles.

I have since developed a great liking for the Ford Endeavour 3.2, having read all about it on this forum and elsewhere. Though I am still a couple of years away from making the purchase (I bought the Duster AWD in August 2016), I have started researching about the Endeavour 3.2, and suddenly the question that struck me was this:

If this vehicle produces 470 NM Torque in the normal gearing, what would it be producing when the 4x4 Low is engaged and also (all other things being equal), would this mean that the Endeavour 3.2 which produces such huge amounts of torque in 4x4 Low mode be a more capable vehicle than the Land Rover Range Rover Autobiography model which though ordinarily produces about 700 Plus NM of Torque but does not have a 4x4 Low, since it is only an AWD vehicle. Underlying thought / question being, in the 4x4 Low mode, is the Ford Endeavour 3.2 more capable as on off-roader than the Land Rover Range Rover Autobiography which would cost 10 times more (approx. 4 Crores or thereabouts)

I am not a subject matter expert (obviously) and hence I did a little research and found the following articles, which as n.devnath says, state that engaging 4x4 Low Range Gearbox produces much greater torque at the wheels (which is the torque relevant to us, if I have understood it correctly).

Sharing the links below:

1. https://jalopnik.com/crawl-ratios-an...eve-1722578417 (See the part where it discusses the Low End Torque)

2. https://www.cartoq.com/10-things-you...el-drive-suvs/ (This article claims that 'the Mahindra Thar has a torque output of 247 Nm when the regular mode is engaged. When the low-gear ratio is engaged, the torque output increases to 600 Nm'.)

3. https://www.outbacktravelaustralia.c...types-examined (This article states that 'It's easy to see why 4WDs need more torque multiplication than road-bound cars. All you have to do is put your front wheels against a steep rock shelf to find out that you need more torque than is available through a road-going transmission. Low-range gearing varies in ratio, but 'real' off-road vehicles have a minimum 2:1 low range reduction, thus at least doubling the torque available. North America’s love of rock-crawling has resulted in some Yank transfer cases with ratios of 4:1.')

4. http://www.4x4abc.com/4WD101/crawl.html (This article states 'Every gear ratio involved subsequently boosts the torque output. This engine produces 200 lbs./ft. of torque - transmission and transfer case multiply it to 2084 lbs./ft. and the differentials boost it further so that each wheel can create a whopping 2141 lbs./ft. of torque. So, the lower a crawl ratio, the higher the torque available at the wheels')

Grateful for all your thoughts / inputs. Please keep them coming."
There has been some discussion on my posts in the said thread with some fellow bhpians disagreeing with the Torque Multiplication bit. But since the articles I have referred state otherwise, I have been referred to this thread to seek opinion of the experts on the Torque Multiplication bit.

Please share your views. Thanks in advance.
Touringlawyer is offline   (1) Thanks Reply With Quote
Old 16th November 2018, 17:45   #272
Team-BHP Support
 
Samurai's Avatar
 
Join Date: Jan 2005
Location: Banglore-Udupi
Posts: 23,723
Thanked: 20,560 Times
Default Re: Torque generation and distribution

Quote:
Originally Posted by Touringlawyer View Post
There has been some discussion on my posts in the said thread with some fellow bhpians disagreeing with the Torque Multiplication bit. But since the articles I have referred state otherwise, I have been referred to this thread to seek opinion of the experts on the Torque Multiplication bit.
Well, you have finally come to the right thread. Lots of people found their fancy ideas about torque destroyed in this thread, when it started nearly 5 years ago.

First thing you need to understand is Torque is a function of load. If there is no load, there is no torque. That means torque generation does change with load.

At neutral gear, engine produces just enough torque to rotate the crankshaft. That could be as less as 5Nm. If you revv in neutral, the crankshaft will turn faster, so it may require 10Nm. Just the additional torque to make it go faster. These are just example figures, will vary from engine to engine.

Useful torque generation starts only once you engage the gears. You start with 1st gear because you want substantial torque at the wheels at lower rpms, to move the car from standing position. For a given gear, the torque becomes a function of rpm, assuming we have load to overcome.

There is a simple way to understand the need for load. Hold a pencil lightly in your left hand (load L1), and try to rotate it using your right hand. You can do it with little force (force F1). Next, hold the pencil tightly in the left hand (load L2). The right hand will require lot more force (force F2) to rotate it. Now, hold the pencil lightly again (L1), try to apply F2 amount of force. You can't... because there is little load. You can't generate torque without a load to overcome.

And yes, gearing ratios do multiply torque at the wheel, while dividing the rpm at the wheel. 4WD 4low ratios are roughly set at 2X. That means, the torque will double at wheel and the rpm at wheel (drive axle) will be halved.

The L in 4L actually means low speed/traction rather than low multiplication ratio. So 4L is actually high ratio/torque. But we are all used to calling it low ratio, which really causes confusion to folks trying to understand it.

Last edited by Samurai : 16th November 2018 at 17:55.
Samurai is offline   (6) Thanks Reply With Quote
Old 16th November 2018, 18:22   #273
BHPian
 
Join Date: Apr 2016
Location: Delhi NCR
Posts: 65
Thanked: 118 Times
Default Re: Torque generation and distribution

Quote:
Originally Posted by Samurai View Post
The L in 4L actually means low speed/traction rather than low multiplication ratio. So 4L is actually high ratio/torque. But we are all used to calling it low ratio, which really causes confusion to folks trying to understand it.
Hey Samurai, first of all, please accept my sincerest gratitude for that lovely explanation, made simple for a newbie like me.

Now for some further query

You say "And yes, gearing ratios do multiply torque at the wheel, while dividing the rpm at the wheel. 4WD 4low ratios are roughly set at 2X. That means, the torque will double at wheel and the rpm at wheel (drive axle) will be halved".

Now if you would kindly refer to the article from outbackaustralia quoted in my post, it says "Low-range gearing varies in ratio, but 'real' off-road vehicles have a minimum 2:1 low range reduction, thus at least doubling the torque available. North America’s love of rock-crawling has resulted in some Yank transfer cases with ratios of 4:1".

So my query is, am I understanding it correctly that going by your explanation and the article from outbackaustralia, if a given vehicle (say Ford Endeavour 3.2) makes 470 NM Peak Torque across a particular range of RPM, in the 4x4 4L mode, depending on the gear one engages, the torque generated would be 2x470, and (just for the sake of assumption), if it had the yank transfer case with ratio 4:1, the torque it would generate in 4L mode would be 4x470?

Many thanks for your patience and time.

Last edited by Samurai : 17th November 2018 at 08:22. Reason: Avoid quoting large posts
Touringlawyer is offline   (1) Thanks Reply With Quote
Old 16th November 2018, 19:19   #274
BHPian
 
roby_dk's Avatar
 
Join Date: Nov 2016
Location: New Delhi
Posts: 655
Thanked: 1,682 Times
Default Re: Torque generation and distribution

To keep it simple and straight is there any situation in which the torque at any wheel can be more than the specified values by manufacturers.

If I talk about figures, considering the above example of Ford Endeavour 3.2 having 470nm of torque can the torque be more than 470 anytime in any mode 4H or 4L. Are there any other SUV's available where this is possible?
roby_dk is offline   (1) Thanks Reply With Quote
Old 16th November 2018, 20:04   #275
Team-BHP Support
 
Samurai's Avatar
 
Join Date: Jan 2005
Location: Banglore-Udupi
Posts: 23,723
Thanked: 20,560 Times
Default

Quote:
Originally Posted by Touringlawyer View Post
So my query is, am I understanding it correctly that going by your explanation and the article from outbackaustralia, if a given vehicle (say Ford Endeavour 3.2) makes 470 NM Peak Torque across a particular range of RPM, in the 4x4 4L mode, depending on the gear one engages, the torque generated would be 2x470, and (just for the sake of assumption), if it had the yank transfer case with ratio 4:1, the torque it would generate in 4L mode would be 4x470?
There are 3 ratios you must worry about when thinking about torque at the wheels. Transmission Gear ratio, Transfer-case gear ratio and Differential gear ratio.

Since I am not familiar with all the gear ratios of Endy 3.2, let me take Gypsy as an example.

Gypsy (MG413W) ratios:
Quote:
Originally Posted by khan_sultan View Post
1st 3.652
2nd 1.947
3rd 1.423
4th 1.000
5th 0.795
Reverse 3.466

TC-High: 1.409
TC-Low: 2.268

Axle: 3.73:1
Looking at the above info, we can say the following:

At 1st gear & 4L, the torque@wheel = 3.652*2.268*3.73*torque@engine = 30.89 * torque@engine. [highest possible gearing in stock Gypsy]
.
.
At 5th gear & 4H, the torque@wheel = 0.795*1.409*3.73*torque@engine = 4.17 * torque@engine. [lowest possible gearing in stock Gypsy]

You can calculate the gearing in all the combinations in-between yourself. Note I have not bothered to mention the actual engine torque. That is because it depends on load.

So if you assume the load to be so high to need the peak torque of the engine at the highest gearing, then the "total torque at wheels" will be highest gearing (30.89) multiplied by peak engine torque (104Nm for Gypsy), which is 3212Nm. Divide by 4 to get 803Nm at each wheel. This will happen only if the traction exists between the tyre and the ground, this represents the load. If the tyre starts slipping, engine will never reach peak torque, and same goes for the wheel torque.

Now, ready for the next shock? The 803Nm/wheel torque is applied at the center of the wheel. The force applied at the ground reduces with increase in radius.

T = F * R or
F = T/R

Force on the tarmac = torque at the center/Radius of the wheel

So, if you install bigger tyres, you reduce the force where tyre hits the ground. Something to keep in mind while upgrading to bigger tyres. It is not just the un-sprung weight, you are also reducing effective force applied on ground due to increase in radius. This is the same reason why Winches have max pulling force when the wheel drum is fully unspooled.

Quote:
Originally Posted by roby_dk View Post
To keep it simple and straight is there any situation in which the torque at any wheel can be more than the specified values by manufacturers.

If I talk about figures, considering the above example of Ford Endeavour 3.2 having 470nm of torque can the torque be more than 470 anytime in any mode 4H or 4L. Are there any other SUV's available where this is possible?
Manufacturers only mention the peak torque possible at the engine. They never mention torque/wheel, it is up to you to calculate by knowing the transmission ratio, TC ratio and axle ratio. I have done that for you using the gypsy example.

Also, in a locked differential, the torque distribution is not equal, only the speed is equal. In an advanced 4WD where all 3 differentials can be locked, each wheel can have different torque input depending on individual wheel traction. Only when front/center/rear differentials are open, the torque distribution is equal. So it is pointless to expect torque at wheel figures.

Last edited by Samurai : 16th November 2018 at 20:07.
Samurai is offline   (7) Thanks Reply With Quote
Old 16th November 2018, 20:10   #276
BHPian
 
Join Date: Apr 2016
Location: Delhi NCR
Posts: 65
Thanked: 118 Times
Default Re: Torque generation and distribution

Hey Samurai, merely clicking thanks for a post like this one does not do justice to the post. So please again accept heartfelt thanks for that amazing explanation.

I had read the exact same thing on the following link (shared earlier):

https://jalopnik.com/crawl-ratios-an...eve-1722578417

Extracting the entire relevant portion below:

Quote:
"Crawl Ratio

A crawl ratio is simply the ratio of torque at the wheels to torque at your engine’s flywheel. It represents how many times your engine torque is multiplied before it gets to the place where the actual propulsion occurs. There are only three components that determine a vehicle’s crawl ratio: transmission, transfer case, and differential (see image above).

Power from the engine goes through the transmission, then through the transfer case, and finally through the differential (sometimes called the “final drive,” because it is the final gear reduction). Power from the engine is conserved — you can’t gain more power by simply going through a set of gears, but you can gain more torque. And since power is proportional to torque x RPM (horsepower = torque*RPM/5252), if you go through a gear reduction and increase your output torque, you have to decrease your RPM by the same ratio to keep your power constant.

As your engine’s power steps its way through the trans, t-case, and diff, it trades angular velocity (RPM) for torque. In other words, each time engine power is sent through a gear reduction (in the transmission, transfer case, and differential), the output speed is lower than the input speed, but the output torque is higher.

So, how do we figure out how much more torque is at the wheels than at the flywheel? Simple. By multiplying engine torque by the gear ratios in the three gear sets, we can arrive at a crawl ratio. In equation form:

crawl ratio = twheels / tflywheel = trans ratio x transfer case ratio x diff ratio

In the equation above, τwheels is the torque at the wheels, τflywheel is the torque leaving the engine and entering the transmission, ntc is the low range gear ratio in the transfer case, ntrans is the first gear ratio in the transmission, and ndiff is the axle ratio.

Example:

A 1992 Jeep Cherokee has an AW4 4-speed automatic transmission with the following gear ratios (first through fourth): 2.80, 1.53, 1.00 & .75. The Jeep is equipped with an NP231 transfer case with a 2.72-to-one “low range” reduction and 3.55 axle ratios.

To calculate the crawl ratio, simply multiply the shortest transmission gear ratio (the one that multiplies the torque most, i.e. first gear) by the low range gear ratio and the axle ratio.

crawl ratio 92xj = 2.80 x 2.72 x 3.55 = 27

By comparison, the new Wrangler Rubicon with a manual transmission has a first gear ratio of 4.46, a 4-to-1 transfer case, and 4.10 axle ratios. This equates to an enormous crawl ratio of 73!

Photo credit: Jeep

Low End Torque


But crawl ratio, by itself, means very little without mentioning engine torque. You need to know what torque you’re actually multiplying by the crawl ratio to really understand how well your vehicle will handle the rough stuff. The crawl ratio of 27 we calculated above for the XJ is perfectly sufficient because the 4.0-liter produces nearly 200 lb-ft of torque at idle. And we know that torque at the wheels is simply the crawl ratio multiplied by engine torque. So, for the XJ, at idle in low range:

twheels = tflywheel x crawl ratio = 200 lb.ft. x 27 = 5400 lb. ft.

That’s a lot of torque at the wheels. That’s good, because not having to rev the engine to produce torque means the Jeep can travel nice and slowly over the rocks. If my XJ had the anemic 2.5-liter inline four, however, the same crawl ratio of 27 would yield much lower torque at the wheels and would make accelerating up rocks a rather pitiful experience. This is why four cylinder XJs came with 4.10 differential gears.

So, torque at the wheels is good, but it doesn’t tell the whole story. Tires also play a big role in gearing, too."
Not extracting the tyre explanation part here as that would make the post even more bulky.

But let me say this, reading on internet from another source is one thing, and reading an explanation from an inhouse expert at TeamBHP gives an altogether different level of comfort and confidence.

You truly made my day. Big thanks again.

Last edited by Samurai : 16th November 2018 at 20:18. Reason: using quote for external article
Touringlawyer is offline   (4) Thanks Reply With Quote
Old 17th November 2018, 10:20   #277
BHPian
 
Join Date: May 2018
Location: Roorkee
Posts: 127
Thanked: 1,163 Times
Default Re: Torque generation and distribution

Quote:
Originally Posted by Samurai View Post
Since I am not familiar with all the gear ratios of Endy 3.2, let me take Gypsy as an example.
Following are the ratios for the Endeavour 3.2 with 6R80 transmission:
1st 4.17
2nd 2.34
3rd 1.52
4th 1.14
5th 0.87
6th 0.69
Reverse 3.40

TC High: 1
TC Low: 2.48

Axle: 3.73

One question - while Torque Converter mainly has losses, it usually has a multiplication factor which at stall speed is as high as 1.8 to 2.5 (as per wikipedia). Would it also be considered while calculating the torque available at wheel?
A.G. is offline   (1) Thanks Reply With Quote
Old 27th November 2018, 21:04   #278
Distinguished - BHPian
 
Join Date: Jul 2009
Location: Calcutta
Posts: 4,055
Thanked: 3,746 Times
Default Re: Torque generation and distribution

^^^
Yes. But remember, it is at stall. And keep in mind transmission fluid getting hot.

Regards
Sutripta
Sutripta is offline   (2) Thanks Reply With Quote
Old 28th November 2018, 10:15   #279
BHPian
 
Join Date: May 2018
Location: Roorkee
Posts: 127
Thanked: 1,163 Times
Default Re: Torque generation and distribution

Quote:
Originally Posted by Sutripta View Post
And keep in mind transmission fluid getting hot.
Right but I guess once in a while to get out of a tricky situation, the heat from the transmission fluid should not matter.
A.G. is offline   Reply With Quote
Old 9th December 2018, 10:00   #280
BHPian
 
Blooming Flower's Avatar
 
Join Date: Apr 2017
Location: Mysore, Kolkata
Posts: 139
Thanked: 690 Times
Default Re: Torque generation and distribution

Posted by Debuda, in other thread as an explanation.
Pasting the link here for continuity and correlation with the topic.

https://www.team-bhp.com/forum/offic...ml#post4499072 (Ford Endeavour : Official Review)
Blooming Flower is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Delhi Meet & Cause Initiative: Blanket and Clothes distribution Drive - 12th Jan @ CP devilwearsprada The Team-BHP Meet Section 80 29th January 2014 09:45
Fiat mulls separate distribution network airbender The Indian Car Scene 5 13th October 2010 21:24
Distribution Block & Fuse Block in Chennai ibm_jennifer In-Car Entertainment 6 31st March 2009 13:59
TATA Motors to hive off Distribution Car-Agey The Indian Car Scene 6 17th July 2008 21:42
Which linux distribution for me? Harrie Shifting gears 3 5th October 2005 16:39


All times are GMT +5.5. The time now is 06:03.

Copyright ©2000 - 2019, Team-BHP.com
Proudly powered by E2E Networks